1. Field of the Invention
The present invention relates to a method of producing thin films and apparatus, such as, a heat treatment apparatus, for producing the same.
2. Description of the Related Art
A vertical type diffusion furnace has been used for forming diffusion layer films. The conventional vertical type diffusion furnace is provided, as main parts, with a furnace core cylinder, a substrate supporting boat, a process gas injector pipe having a lot of holes and disposed in the furnace core cylinder, a purge gas supply tube and a heat insulating cylinder. A lot of substrates can be mounted on the substrate supporting boat, which is provided with a mechanism to make the boat to rotate together with the heat insulating cylinder around a center axis or line of the heat insulating cylinder as a rotation axis.
In forming a diffusion layer film on the substrate by the use of this conventional vertical type furnace, a process gas is supplied from many blowing holes provided at the process gas injector pipe toward the center line of the rotation axis, so that the gas flow is made parallel to the surface of each substrate.
The process gas is supplied on the substrate from the process gas injector pipe and is spouted toward the center of the substrate by being spread perpendicular to the spouting direction of the process gas in the conventional vertical type diffusion furnace. Since the substrate is rotated by the boat rotating mechanism, a small amount of the process gas tends to be supplied at the peripheral area of the substrate while a large amount of the gas is supplied at the center of the substrate.
Accordingly, the thin film thus formed has the film thickness, which has a tendency to have a hill-like film thickness distribution in which the film thickness is gradually increased from the peripheral region to the center of the substrate with exhibiting a deficiency to become large at the center of the substrate.
Accordingly, it is an object of the present invention to provide a method for forming thin films capable of providing a uniform film thickness on the substrate.
It is another object of the present invention to provide an apparatus for practicing the method for forming the thin film described above.
According to one aspect of the present invention, there is provided a method of producing a thin film on a substrate disposed in a furnace core pipe, which comprises a step of making the substrate to rotate around a center axis in accompany with allowing a first gas to spout toward the substrate. The center axis is a normal line passing through the center of one principal face of the substrate. The first gas consists essentially of a process gas. In the method of the aspect of the present invention, the thin film is formed on the substrate while allowing a second gas to spout via the center axis in the colliding direction to the first gas. The second gas consists essentially of an inert gas or nitrogen gas.
It is preferable that the second gas spouts along a direction approximately opposite to the spout direction of the first gas.
It is more preferable that the locations for supplying the first gas and the second gas are approximately symmetrically positioned with each other with respect to the center axis. The first gas is simultaneously supplied with the second gas.
According to another aspect of the present invention, there is provided an apparatus for producing thin films, which comprises a furnace core pipe, a substrate supporting boat for supporting a lot of substrates disposed in the furnace core pipe, a first gas injector pipe having many first blowing holes for spouting the first gas comprising a process gas toward the substrate, the supporting boat having a rotation mechanism for allowing the boat to rotate using a normal line passing through the center of a principal face of the substrate as a rotation axis, and a second gas injector pipe having second blowing holes for spouting a second gas and being provided at an opposite position at which the second gas collides with the first gas on a surface of the substrate. The second gas consists essentially of an inert gas or nitrogen gas.
It is preferable that the first gas injector pipe is provided at an approximately symmetrical position against the second gas injection pipe relative to the center line of the rotation axis.
More preferably in the aspect of the present invention, the first and the second gas injector pipes makes a pair of pipes as a first pair of pipes. The apparatus further comprises another pair of pipes similar to the first pair of pipes as a second pair of pipes. Each of the second pair of pipes is provided in a different position from the first pair of pipes but has the same position relation relative to the center line as the first pair of pipes.